Manipulating polaritons at the extreme scale in van der Waals materials

Polaritons, originating from the interactions between photons and material excitations, have attracted attention because of their strong field compression and deeply subdiffractional scales. For practical applications, it is crucial to manipulate polaritons efficiently, but doing so has remained challenging because of the relatively poor tunability of traditional polaritonic media. Fortunately, in the past decade, polaritons hosted by van der Waals (vdW) materials have allowed new opportunities to tackle this difficulty. We review the state of the art in the manipulation of polaritons at the extreme scale in vdW materials. Benefiting from the large and expanding catalogue of vdW materials and associated architectures and techniques, more accessible manipulation strategies are expected, not only offering control of light at the nanoscale with new degrees of freedom, but also offering insight into nanophotonics, meta-optics, topological physics and quantum materials. Polaritons enable the precise control of light at an extreme scale. Van der Waals (vdW) materials offer a natural and versatile platform to host and tailor polaritons. This Technical Review summarizes the state of the art in the manipulation of polaritons with vdW materials. Key points Van der Waals materials and relevant techniques make it possible to engineer polaritons conveniently and effectively at the deep-subwavelength scale. The inherent properties of polaritonic materials play a dominant role in polariton behaviours, because of the part-light, part-matter nature of polaritons. Owing to tight electromagnetic field compression, polaritons are highly sensitive to various physical stimuli. The dispersion relations of polaritons indicate potential tuning pathways, such as dielectric environment. Combining individual polariton modes, regardless of their types, can greatly enrich the toolbox for polariton manipulation.